U.S. patent number 4,415,630 [Application Number 06/470,180] was granted by the patent office on 1983-11-15 for process of making magnetic recording medium.
This patent grant is currently assigned to TDK Electronics Co., Ltd.. Invention is credited to Yuichi Kubota, Masaharu Nishimatsu, Kazushi Tanaka.
United States Patent |
4,415,630 |
Kubota , et al. |
November 15, 1983 |
Process of making magnetic recording medium
Abstract
A magnetic recording medium comprises a substrate and a magnetic
recording layer formed thereon and which is made of a magnetic
coating material consisting essentially of a magnetic powder
dispersed in a binder, the coating material containing a titanium
coupling agent. The magnetic powder is coated with the coupling
agent or is mixed with the agent and then dispersed in the binder.
The binder is prepared by mixing and plasticizing a
radiation-sensitive modified resin with a radiation-sensitive soft
resin and subjecting the mixture to radiation cross-linking and
polymerization. Process for producing the medium comprises coating
the magnetic particles with the titanium coupling agent, blending
the coated particles with the binder to form a magnetic coating
material, and then applying the material to the substrate.
Alternatively, the process comprises mixing the titanium coupling
agent with the magnetic particles, blending the mixture with the
binder, and then applying the resulting coating material to the
substrate. The titanium coupling agent is used in an amount of
0.5-7 wt %, preferably 0.5-3 wt %, based on the weight of the
magnetic powder.
Inventors: |
Kubota; Yuichi (Tokyo,
JP), Nishimatsu; Masaharu (Tokyo, JP),
Tanaka; Kazushi (Tokyo, JP) |
Assignee: |
TDK Electronics Co., Ltd.
(Tokyo, JP)
|
Family
ID: |
26419310 |
Appl.
No.: |
06/470,180 |
Filed: |
February 28, 1983 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
269391 |
Jun 1, 1981 |
|
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Jun 10, 1980 [JP] |
|
|
55-78223 |
Jun 10, 1980 [JP] |
|
|
55-78227 |
|
Current U.S.
Class: |
428/403; 427/127;
427/128; 427/216; 427/221; 427/385.5; 427/388.1; 428/457; 428/500;
428/522; 428/842.2; 428/900; 930/DIG.630; G9B/5.271; G9B/5.276 |
Current CPC
Class: |
G11B
5/708 (20130101); G11B 5/712 (20130101); Y10S
428/90 (20130101); Y10T 428/2991 (20150115); Y10T
428/31678 (20150401); Y10T 428/31855 (20150401); Y10T
428/31935 (20150401) |
Current International
Class: |
G11B
5/708 (20060101); G11B 5/712 (20060101); B32B
005/16 (); H01F 010/02 () |
Field of
Search: |
;427/44,127,128,216,221,385.5,388.1
;428/403,457,500,522,694,900 |
Primary Examiner: Pianalto; Bernard D.
Attorney, Agent or Firm: Wyatt, Gerber, Shoup, Scobey &
Badie
Parent Case Text
This is a continuation of application Ser. No. 269,391 filed June
1, 1981, abandoned.
Claims
What we claim is:
1. A magnetic recording medium comprising a substrate and a
magnetic recording layer formed thereon, characterized in that said
magnetic recording layer is made of a magnetic coating material
consisting essentially of a magnetic powder dispersed in a binder,
said magnetic coating material containing a titanium coupling
agent.
2. A magnetic coating medium according to claim 1, wherein said
magnetic powder has a surface coating of said titanium coupling
agent.
3. A magnetic recording medium according to claim 1, wherein said
magnetic powder is mixed with said titanium coupling agent and then
dispersed in said binder.
4. A magnetic recording medium according to claim 1, 2 or 3,
wherein said binder is one prepared by mixing and plasticizing a
radiation-sensitive modified resin, which has radiation-sensitive,
unsaturated bonds, such as acrylic, maleic, or allylic double
bonds, and adapted to be cross-linked and polymerized by exposure
to radiation, with a radiation-sensitive soft resin, which also has
said double bonds, or a prepolymer, oligomer, or telomer thereof
(with a dynamic modulus of less than 1.times.10.sup.9 dyn/cm.sup.2
at 20.degree. C.) and then by subjecting the mixture to radiation
cross-linking and polymerization.
5. A magnetic recording medium according to any of claims 1 to 4,
wherein said magnetic powder is in the form of acicular particles
of a cobalt-modified magnetic iron oxide and/or particles of a
magnetic alloy.
6. A magnetic recording medium according to claim 4 or 5, wherein
said cross-linking and polymerization by irradiation are carried
out in an inert gas stream.
7. A process for producing a magnetic recording medium which
comprises the steps of coating magnetic particles with a titanium
coupling agent, blending the coated magnetic particles with a
binder to obtain a magnetic coating material, and then applying the
coating material to a substrate.
8. A process according to claim 7, which further comprises the step
of drying the coated surfaces, after the coating of said magnetic
particles with said coupling agent and before blending said coated
particles with said binder resin.
9. A process for producing a magnetic recording medium which
comprises the steps of mixing a titanium coupling agent with
magnetic particles, blending the magnetic particles so mixed with
said coupling agent with a binder to obtain a magnetic coating
material, and then applying the coating material to a
substrate.
10. A process according to claim 7, 8, or 9, wherein said titanium
coupling agent is used in an amount of 0.5-7 weight percent based
on the weight of said magnetic particles.
11. A process according to claim 7, 8 or 9, wherein said titanium
coupling agent is used in an amount of 0.5-3 weight percent based
on the weight of said magnetic particles.
Description
BACKGROUND OF THE INVENTION
This invention relates to improvements in a magnetic recording
medium for use in the form of a video tape, computer tape, high
performance sound recording tape, multicoat tape, magnetic disk,
floppy disk, magnetic card, or the like.
Magnetic recording materials for those applications generally use a
thermosetting binder, and a three-dimensional network structure is
formed by a chemical reaction of a cross-linking agent, such as a
polyisocyanate-radical-containing compound, with reactive
functional groups, such as hydroxyl, amino, or the like, in the
binder. The formation of the structure is intended to prevent the
magnetic recording layer from coming off and to improve the
durability, running properties, and environmental reliability of
those magnetic media. Also, the conventional media employ a silane
coupling agent for the purpose of organic or inorganic complexing
or compounding. With a coupling agent of the kind, however, it is
still impossible to obtain satisfactory dispersion of an inorganic
solid powder in magnetic pigments which contain such ferromagnetic
metals as Fe, Co, and Ni. As a consequence, the bonds between the
magnetic material and the binder and between the magnetic recording
layer and the substrate are insufficient and weak, causing a
progressive and rapidly intensified tendency of dropouts from the
both edges inwardly of the tape as it runs past the record or play
head.
BRIEF SUMMARY OF THE INVENTION
This invention has for its object the provision of a magnetic
recording medium improved in surface properties to such an extent
that it can overcome the afore-described difficulties.
The magnetic recording medium according to the invention uses a
titanium coupling agent for the coupling purpose, as mixed with
magnetic particles, a binder, and also other additives, such as an
antistatic agent, lubricant, and organic solvent, so as to improve
the wear resistance and decrease the friction of the medium with
respect to head recorder systems.
The titanium coupling agent that the present invention adopts
features six different functions as will be expected from its
molecular structure. With a chemical structure ##STR1## it is
polyfunctional in contrast to the silane coupling agent and attains
a new, modifying coupling effect.
Function (1): (RO).sub.M --Chemically combines with an inorganic
substance.
Function (2): ----Undergoes transesterification, bridging, and
hardening.
Function (3): OX.sup.1 --This group combines with titanium as a
nuclei and influences all other functions.
Function (4): R.sup.2 --A group for inducing molecular entanglement
in a long chain; it exhibits a behavior like a plastic polymer.
Function (5): Y--Reactive and bridges and hardens, behaving like a
thermosetting polymer.
Function (6): N--Polyfunctional and behaves like thermoplastic and
thermosetting polymers.
These characteristic functions are extremely useful in improving
the adhesion of the magnetic layer to the base, fluidity and hence
coatability of the magnetic coating on account of the plastic
behavior, wear resistance with strengthened bond between the
magnetic powder and the binder, and dispersibility of the magnetic
particles; in economizing in the solvent thanks to the higher
solids content of the coating composition; and in preventing the
dropouts of the magnetic recording layer with repeated usage. With
these and other advantages the titanium coupling agent makes it
possible to obtain an ideal magnetic recording medium. The agent is
used in an amount ranging from 0.5 to 7% by weight, preferably from
0.5 to 3% by weight, based on the weight of the magnetic
powder.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing rates of signal attenuation with
time;
FIG. 2 is a graph showing changes in friction on a video tape
recorder with the tape running time;
FIG. 3 is a graph showing the relation between the peak voltage of
reproduction output and the number of passes;
FIG. 4 is a graph showing rates of signal attenuation with time;
and
FIG. 5 is a graph showing changes in friction on a video tape
recorder with the tape running time.
DETAILED DESCRIPTION OF THE INVENTION
The invention is illustrated by the following examples. Examples 1
and 2 describe the procedures in which a magnetic powder is first
wetted with a coupling agent and then mixed with a binder.
EXAMPLE 1
A composition consisting of
______________________________________ Acicular magnetic powder of
.gamma.-Fe.sub.2 O.sub.3 120 parts (major axis 0.5.mu., minor axis
0.07.mu., Hc 400 Oe) Titanium coupling agent (marketed by 4 parts
Kenrich Petrochemicals, Inc. under the trade designation "KR-38S")
Solvent 100 parts (Methyl ethyl ketone/toluene 50/50)
______________________________________
was mixed by a powerful mixer for 3 hours, so that the acicular
magnetic iron oxide was thoroughly wetted with the coupling agent.
Next,
______________________________________ Vinyl chloride-vinyl
acetate-vinyl 24 parts alcohol copolymer resin (Union Carbide
Corp.'s "VAGH") Polyurethane resin (Nippon Polyurethane 10.3 parts
Ind. Co.'s "Nippollan 5033" in a 45% ethyl acetate-toluene
solution, in terms of 100% solids) Methyl ethyl ketone 250 parts
Methyl isobutyl ketone 150 parts
______________________________________
were mixed well and dissolved on an agitator into a lacquer.
Together with the .gamma.-Fe.sub.2 O.sub.3 particles wetted with
the titanium coupling agent, the lacquer was placed in a ball mill
and was mixed for 24 hours to effect thorough dispersion of the
.gamma.-Fe.sub.2 O.sub.3 particles.
Then, after the addition of 3 parts behenic acid, the dispersion
was continued for one more hour, and a magnetic coating material
was prepared. It was coated on a polyester film and, following the
necessary finish, the coated film was slitted into a ribbon 3.8 mm
wide as an audio cassette tape for 90-minute recording or playback
(Specimen 1).
COMPARATIVE EXAMPLE 1
An audio cassette tape (Specimen A) was made by the same procedure
as described in Example 1 with the exception that the titanium
coupling agent was replaced by a silane one (UCC's "A-1126"). The
characteristics of the tapes according to Example 1 and Comparative
Example 1 were as summarized in Table 1.
______________________________________ Deg. of Running Audio sen-
Audio Spec- Surface orien- dura- sitivity MoL imen quality.sup.1
tation.sup.2 bility.sup.3 12.5 KHz 333 Hz.sup.4
______________________________________ 1 10.0 2.10 Over +3.0 +1.5
100 hrs. A 7.0 1.52 Stops after -1.0 -1.5 10 hrs.
______________________________________ Remarks: .sup.1 The surface
gloss value as measured on the basis of a reference glass plate
which is set at zero decibel (dB). .sup.2 Measured with the
application of a magnetic field of 5000 gauss, b means of Toei
Kogyo's orientation meter, Model VSMIII, at Br 1/11. .sup.3
Determined with Matsushita Communication Ind. Co.'s car stereo set
Model CX1147P, at an ambient temperature of 50.degree. C. and
relative humidity of 70%. .sup.4 Comparative values measured by
Nakamichi's deck, Model 1000, on th basis of TDK's standard tape
set at 0.0 dB.
As will be appreciated from Table 1, the titanium coupling agent's
effect as a dispersant combined with its favorable effect on the
fluidity of the coating material to improve the surface quality and
magnetic orientation of the resulting tape. Accordingly, the audio
electromagnetic conversion characteristics, such as the audio
sensitivity at 12.5 KHz and MoL at 333 Hz, were satisfactory.
Further, the force of binding of the titanium coupling agent with
the .gamma.-Fe.sub.2 O.sub.3 particle surfaces enhanced the
strength of the magnetic layer, and the cassette tape according to
the invention exhibited excellent running durability under the
rigorously hot and humid conditions of 50.degree. C. and 70%
RH.
EXAMPLE 2
A composition consisting of
______________________________________ Acicular magnetic powder of
Fe alloy 120 parts (major axis 0.3.mu., minor axis 0.04.mu., Hc
1100 Oe) Titanium coupling agent 3.6 parts (Kenrich's "KR-38S")
Solvent 100 parts (methyl ethyl ketone/toluene 50/50)
______________________________________
was mixed by a powerful mixer for 3 hours and the acicular magnetic
iron oxide was wetted well with the coupling agent. Next, the
mixture was mixed by a high speed mixer for 70 minutes with
______________________________________ Polyvinyl butyral resin
(marketed by 15 parts Sekisui Chemical Co. under the by weight
trade mark "BMS") Thermoplastic urethane (marketed by 15 parts B.
F. Goodrich Chemical Co. under by weight the trade mark "Estane
5715") Solvent (methyl ethyl ketone) 200 parts by weight Lubricant
(higher fatty acid-modified 3 parts silicone oil) by weight
______________________________________
and dispersion was effected by means of a sand mill for 4 hours.
After the dispersion, 5 parts by weight, in terms of solids, of an
isocyanate compound ("Desmodur L" made by Bayer AG.) capable of
cross linking by a reaction with the functional groups composed
mostly of the hydroxyl groups of the binder in the magnetic coating
material was added to the coating composition already charged in a
sand grinding mill, and the mixture was kneaded for 20 minutes. The
magnetic coating material thus obtained was applied to a 15
.mu.-thick polyester film. Following the treatments of the coated
film for magnetic field orientation, solvent drying, and surface
smoothening, the film was held in a heat-treating oven at
80.degree. C. for 48 hours to effect thermal curing. This film of
Example 2 was slitted into a video tape (Specimen 2).
COMPARATIVE EXAMPLE 2
The procedure of Example 2 was repeated with the exception that a
silane coupling agent (UCC's "A-1120") was employed instead of the
titanium coupling agent, and a video tape (Specimen B) was made.
The specimens of Example 2 and Comparative Example 2 were tested,
and the results as given in Table 2 were obtained.
TABLE 2 ______________________________________ Repeat- ed run Sur-
dura- Drop- face Electromagnetic bility.sup.3 out Bond Spec- quali-
convern. charac..sup.2 40.degree. C. No./ str..sup.5 imen ty.sup.1
MHz Y S/N 60% RH min.sup.4 (g)
______________________________________ 2 12.0 0 0 >200 0.6 60
runs (recipro.) B 6.5 -15 dB -10 dB 80 runs 5 5 (recipro.)
______________________________________ Remarks: .sup.1 The surface
gloss value as measured on the basis of a reference glass plate
which is set at zero decibel (dB). .sup.2 Determined by means of
Matsushita Electric's video tape recorder, Model National Maclord
6600. .sup.3 Determined by means of Matsushita Electric's video
tape recorder, Model National Maclord 6600. .sup.4 Determined by
means of Matsushita Electric's video tape recorder, Model National
Maclord 6600. .sup.5 Bonding strength as measured by a test for
stripping the coating away from the base under tension.
As is obvious from Table 2, the video tape Specimen 2 was superior
to Specimen B in all the test items. It exhibited particularly good
adhesion or bonding strength and very few occurrences of
dropout.
An example in which magnetic particles were coated with a coupling
agent prior to the mixing with a binder is given below.
EXAMPLE 3
______________________________________ Acicular magnetic particles
of Fe alloy 120 parts (major axis 0.3.mu., minor axis 0.04.mu., Hc
1100 Oe) Titanium coupling agent 3.6 parts (Kenrich's "KR-38S")
Methyl ethyl ketone 1000 parts
______________________________________
These components, including the magnetic powder, were placed
simultaneously or in succession into a mixer or blender and were
stirred and mixed for 8 hours, so that the titanium coupling agent
was adsorbed on the surface of the magnetic particles. The
agitation mixer to be employed may be any of known apparatuses,
such as a roll mill, ball mill, high speed impeller disperser,
homogenizer, or ultrasonic dispersion machine.
The thoroughly stirred and mixed magnetic particles were spread and
dried with heat, e.g., at a temperature between 40.degree. and
100.degree. C. for about 30 minutes to 100 hours. In this way the
magnetic particles were coated with the titanium coupling
agent.
Following this precoating,
______________________________________ Precoated acicular magnetic
120 parts particles of Fe alloy by weight Solvent 300 parts (methyl
ethyl ketone/toluene 50/50) by weight Polyvinyl butyral 15 parts by
weight ______________________________________
were mixed by a high speed mixer for 70 minutes, and the mixture
was dispersed by a sand mill for 4 hours. After the dispersion, 5
parts by weight, in terms of solids, of an isocyanate compound
("Desmodur L" made by Farbenfabriken Bayer AG) capable of
cross-linking by a reaction with the functional groups composed
mostly of the hydroxyl groups of the binder in the magnetic coating
material was added to the coating composition already charged in a
sand grinding mill, and the mixture was kneaded for 20 minutes. The
magnetic coating material so obtained was applied to a 15
.mu.-thick polyester film, and the coated film was treated for
magnetic field orientation, solvent drying, and surface
smoothening, and then was held in a heat-treating oven at
80.degree. C. for 48 hours to effect thermal curing. This magnetic
recording medium of Example 3 was slitted into a video tape
(Specimen 3).
Test results of this Specimen 3 are given in Table 3, by way of
comparison, together with those of Specimen 2 of Example 2.
TABLE 3 ______________________________________ Sur- Repeated run
De- face Electromagnetic durability.sup.3 posit Bond Spec- quali-
convern. charac..sup.2 40.degree. C. on str..sup.5 imen ty.sup.1 4
MHz Y S/N 60% RH head.sup.4 (g)
______________________________________ 3 15.0 +0.5 +2.5 >200
runs 4.5 75 (recipro.) 2 12.0 0 0 >200 runs 4 60 (recipro.)
______________________________________ Remarks: .sup.1 The surface
gloss value as measured on the basis of a reference glass plate
which is set at zero decibel (dB). .sup.2 Determined by means of
Matsushita Electric's video tape recorder, Model National Maclord
6600. .sup.3 Determined by means of Matsushita Electric's video
tape recorder, Model National Maclord 6600. .sup.4 Determined by
means of Matsushita Electric's video tape recorder, Model National
Maclord 6600. .sup.5 Bonding strength as measured by a test for
stripping the coating away from the base under tension.
It will be understood from Table 3 that the coating composition
using the magnetic particles precoated with the titanium coupling
agent produces a greater intra-film strength or bonding strength
and less deposit on the head than does the composition in which the
magnetic particles are simply blended with the binder. With better
surface quality, the specimen of this example exhibited improved
electromagnetic conversion characteristics, both at RF 4 MHz and in
S/N ratio.
Next, the invention will be described in connection with examples
in which the magnetic particles and the titanium coupling agent are
used with a radiation-sensitive binder synthesized in the manner
now to be explained.
In the following examples, a radiation-sensitive modified resin and
a radiation-sensitive elastomer are combined for use as a binder
for a magnetic recording medium. For the purposes of the invention
the "radiation-sensitive modified resin" is desired to be one
which, in the premodification state, exhibits a dynamic elastic
modulus at 100 Hz of not lower than 1.0.times.1.0.sup.9
dyn/cm.sup.2 at a temperature between 20.degree. and 60.degree. C.
Also, the term "radiation-sensitive, solvent-soluble elastomer" as
used herein means an elastomer or a prepolymer, oligomer, or
telomer thereof having, as a synthetic rubber, excellent
rubber-like elasticity, flexibility, and adhesion to the polyester
base. It should have dynamic properties such that its dynamic
modulus at 100 Hz is less than 1.0.times.1.0.sup.9 dyn/cm.sup.2 in
the temperature range of 20.degree.-60.degree. C.
Such a thermoplastic resin and a solvent-soluble elastomer are
modified for radiation sensitivity, as will be described, to
produce a cross-linked structure by radical formation on
irradiation. After the modification for radiation sensitivity, the
plastic component and the elastomer or its prepolymer, oligomer, or
telomer are desired to be compatible, from the viewpoint of the
dispersion of fine magnetic particles.
The resinous component and the elastomeric component thus modified
for radiation sensitivity are combined, and the resultant is
utilized as a binder which forms a three-dimensional network
structure upon irradiation. The employment of this binder has
proved extremely effective in stabilizing the electromagnetic
conversion characteristics of the magnetic recording medium for use
in audio, video, memory, measurement, and various other
applications. It has also been very effective in maintaining the
varied physical properties required of the magnetic coating film,
e.g., hardness, flexibility, abrasion resistance, proper friction
coefficient, freedom from the "stickslip" phenomenon, surface
moldability, adhesion to the base, and modulus of elasticity, under
diversified environmental conditions from low to high temperatures
and from low to high humidities.
Thermoplastic resins which can be effectively modified for
radiation sensitivity in the examples to be given later include the
following synthetic resins for paints:
(I) Vinyl chloride-base copolymers
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl
chloride-vinyl alcohol copolymer, vinyl chloride-vinyl
alcohol-vinyl propionate copolymer, vinyl chloride-vinyl
acetate-maleic acid copolymer, and vinyl chloride-vinyl
acetate-end-OH-side-chain alkyl radical copolymer, e.g., UCC's
"VROH", "VYNC", "VYEGX", "VERR", etc.
Especially where a radiation-sensitive modified vinyl chloride-base
copolymer is used by exposure to a low dosage of not more than 20
mrads, it has been confirmed that radicals are formed by some
reaction upon the irradiation in addition to the radical reaction
that results from the radiated functional groups of acrylic double
bonds and the like, although the reaction system is yet to be
clarified, with the consequence that a cross-linked structure is
formed and the binder acts effectively as such for the magnetic
recording medium. Further, it is important to effect the
radiation-sensitive modification of the copolymer by introducing
acrylic double bonds, maleinc acid double bonds, or acrylic double
bonds into the copolymer by a technique to be described later.
(II) Saturated polyester resins
Saturated polyester resins prepared by the ester linkage of a
saturated polybasic acid, such as phthalic acid, isophthalic acid,
terephthalic acid, maleic acid, maleic acid derivative, succinic
acid, adipic acid, or sebacic acid, with a polyhydric alcohol, such
as ethylene glycol, diethylene glycol, glycerin,
trimethylolpropane, 1,2-propylene glycol, 1,3-butanediol,
dipropylene glycol, 1,4-butanediol, 1,6-hexanediol,
pentaerythritol, sorbitol, neopentyl glycol, or
1,4-cyclohexanedimethanol; and resins (e.g., "Vylon 53S") prepared
by modifying the above-mentioned polyester resins with SO.sub.3 Na
or the like to improve their affinity for magnetic particles. It is
essential to modify such a resin by a technique to be described
later to make it sensitive to radiation.
(III) Unsaturated polyester resins
Polyester compounds containing radiation-setting, unsaturated
double bonds in the molecular chain. They may include, e.g., the
unsaturated polyester resins formed by the ester linkage of a
polybasic acid and a polyhydric alcohol, mentioned as thermoplastic
resins in (II) above, part of the polybasic acid being maleic acid,
and containing radiation-setting, unsaturated double bonds; or
prepolymers or oligomers of those resins.
The polybasic acid and polyhydric alcohol components of the
saturated polyester resins may be the compounds referred to in (I)
above, and examples of the radiation-setting, unsaturated double
bonds are maleic acid and fumaric acid.
The radiation-setting, unsaturated polyester resins are prepared by
adding maleic acid, fumaric acid or the like to at least one
polybasic acid component and at least one polyhydric alcohol
component, and treating the mixture in the usual manner, i.e.,
effecting a dehydration or dealcoholization reaction in the
presence of a catalyst and in a nitrogen atmosphere at
180.degree.-200.degree. C., and increasing the temperature to the
range of 240.degree.-280.degree. C., and then subjecting the
resultant to a condensation reaction under a reduced pressure of
0.5-1 mm Hg. In this way the objective polyester resin is obtained.
The product may contain maleic acid, fumaric acid or the like in
the range of 1-40 molar %, preferably 10-30 molar %, on the basis
of the total acid quantity, depending on the cross-linking
condition during the manufacture, radiation-setting and other
properties of the product.
(IV) Polyvinyl alcohol resins
Polyvinyl alcohol, butyral resin, acetal resin, formal resin, and
copolymers of those components are satisfactorily affinitive for
magnetic particles. It is important to modify the hydroxyl groups
contained in those resins by a technique to be described later so
as to make them sensitive to radiation.
(V) Epoxy and phenoxy resins
Epoxy resins obtained by the reaction of bisphenol A with
epichlorohydrin or methyl epichlorohydrin, made by Shell Chemical
Co. (under the trade marks "Epikote 152, 154, 828, 1001, and
1007"), by The Dow Chemical Co. ("DEN 431", "DER 732", "DER 511",
and "DER 331"), and by Dainippon Ink & Chemicals, Inc.
("Epichlon 400" and "Epichlon 800"). Also, the products more highly
polymerized than the abovementioned epoxy resins, e.g., UCC's
phenoxy resins ("PKHA", "PKHC", and "PKHH") and copolymers of
brominated bisphenol A and epichlorohydrin, e.g., Dainippon Ink's
products ("Epichlon 145, 152, 153, and 1120") are useful.
(VI) Cellulose derivatives
Cellulose derivatives of varied molecular weights, too, are
effective as thermoplastic components. Of those, particularly
effective and desirable are nitrocellulose, cellulose
acetobutyrate, ethyl cellulose, butyl cellulose, and acetyl
cellulose. Even more effective is effecting the modification for
radiation sensitivity by utilizing the hydroxyl groups in the resin
in conformity with the procedure to be described later.
(VII) Polyester resins
Examples are the compounds containing one or more hydroxyl groups,
available in the form of polyfunctional polyethers, e.g., "ADEKA
Polyether P-700", "ADEKA Polyether P-1000" and "ADEKA Polyether
G-1500" (all made by Asahi Denka Kogyo K. K.) and "Polymeg 1000"
and "Polymeg 650" (both made by The Quaker Oats Co.).
(VIII) Polycaprolactones
Examples are the polyfunctional polyesters, e.g., "Polycaprolactone
PCP-2000", "Polycaprolactone PCP-0240", and "Polycaprolactone
PCP-0300" (made by Chisso Corp.).
Other effective thermoplastics include polyetherester resins,
polyvinyl pyrrolidone resins and their derivatives (PVP-olefin
copolymers), polyamide resins, polyimide resins, phenol resins,
spiroacetal resins, and acrylic resins containing as a polymeric
component at least one of acrylic esters and methacrylic esters.
They can be made more effective by the radiation-sensitive
modification.
On the other hand, the thermoplastic elastomers or prepolymers to
be combined with the thermoplastic resins are as follows:
(I) Polyurethane Elastomers and their Prepolymers and Telomers
Among thermoplastic elastomers, urethane compounds are particularly
suitable because they are well balanced in properties, imparting
excellent abrasion resistance to magnetic coating films, exhibiting
desirable adhesion to PEP films, and are capable of thoroughly
wetting magnetic particles, thus meeting the essential requirements
of a magnetic recording medium.
Useful as examples of those urethane compounds are the polyurethane
elastomers and their prepolymers and telomers, which are the
products of condensation of various polyvalent isocyanates, such as
2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,3-xylene
diisocyanate, 1,4-xylene diisocyanate, 1,5-naphthalene diisocyanate
m-phenylene diisocyanate, p-phenylene diisocyanate,
3,3'-dimethyl-4,4'-diphenylmethane diisocyanate,
4,4'-diphenylmethane diisocyanate, 3,3'-dimethylbiphenylene
diisocyanate, 4,4'-biphenylene diisocyanate, hexamethylene
diisocyanate, isophorone diisocyanate, dicyclohexylmethane
diisocyanate, "Desmodur L", and "Desmodur N", with various linear
saturated polyesters (formed by condensation of a polyhydric
alcohol, such as ethylene glycol, diethylene glycol, glycerin,
trimethylolpropane, 1,4-butanediol, 1,6-hexanediol,
pentaerythritol, sorbitol, neopentyl glycol, or 1,4-cyclo
hexanedimethanol, with a saturated polybasic acid, such as phthalic
acid, isophthalic acid, terephthalic acid, maleic acid, succinic
acid, adipic acid, or sebacic acid), linear saturated polyethers
(polyethylene glycol, polypropylene glycol, and polytetraethylene
glycol), caprolactams, or with various polyesters, such as
hydroxyl-containing acrylic ester and hydroxyl-containing
methacrylic ester.
While these elastomers may be directly combined with various
radiation-sensitive modified thermoplastics, it is very effective
to modify them to be radiation-sensitive by a reaction with a
monomer having acrylic or allylic double bonds reactive with the
isocyanate or hydroxyl end groups of the particular urethane
elastomer.
(II) Acrylonitrile-Butadiene Copolymer Elastomers
The acrylonitrile-butadiene copolymer prepolymers having a hydroxyl
end group and marketed as "Poly-B-D Liquid Resins" by Sinclair
Petrochemicals, Inc. and the elastomers "Hycar 1432J", etc. by
Nippon Zeon Co. are suitable as the elastomer components in which
the double bonds of the butadiene, in particular, form radicals
upon irradiation to effect cross linking and polymerization.
(III) Polybutadiene Elastomers
Sinclair Petrochemicals' "Poly-B-D Liquid Resin R-15" and other
low-molecular-weight, end-hydroxyl-containing prepolymers are
particularly desirable because of their compatibility with
thermoplastics and their affinity for magnetic particles. The
prepolymer "R15" has hydroxyl end groups, and therefore its
radiation sensitivity can be increased by adding acrylic
unsaturated double bonds to the molecular ends. The product will be
all the more useful as a binder component.
A cyclization product of polybutadiene, e.g., "CBR-M901" marketed
by Japan Synthetic Rubber Co., also displays excellent properties
when it is combined with a thermoplastic resin. Particularly, the
cyclized polybutadiene possesses excellent properties as a binder
component, since if efficiently undergoes the cross-linking
polymerization upon irradiation, with free radical formation from
the unsaturated bonds that originate in the polybutadiene.
Of other thermoplastic elastomers and their prepolymers, the
elastomers of chlorinated rubbers, acrylic rubbers, isoprenes, and
their cyclization products (e.g., Japan Synthetic Rubber's
"CIR701"), epoxy-modified rubbers, and internally-plasticized,
saturated linear polyesters (e.g., Toyobo Co.'s "Vylon #300") can
be effectively used after subjection to the treatment for
radiation-sensitive modification as will be described below.
Typical of the methods for radiation-sensitive modifications
involves introduction into the molecules of the elastomers the
groups that can be cross-linked or polymerized and dried by
irradiation, e.g., acrylic double bonds as of acrylic acid,
methacrylic acid, or an ester compound thereof, allylic double
bonds as of diallyl phthalate, or unsaturated bonds as of maleic
acid or maleic acid derivative, all of which are unsaturated double
bonds adapted for radical polymerization.
Other unsaturated double bonds may be employed provided they can be
cross-linked and polymerized by exposure to radiation.
To be more concrete, the practical procedures for modification for
radiation sensitivity are as follows:
(I) A polyisocyanate compound is reacted with a thermoplastic resin
or a thermoplastic elastomer or prepolymer having one or more
hydroxyl groups in the molecule at a rate of one or more molecules
of the isocyanate group of the former to a molecule of the latter.
Next, the resultant is reacted with a monomer having groups
reactive to the isocyanate group and also having unsaturated double
bonds that harden upon irradiation at a rate of one molecule of the
former to one or more molecules of the latter. The reaction
product, e.g., a saponified vinyl chloride-vinyl acetate copolymer
(UCC's "VAGH"), is again reacted with toluene diisocyanate at a
rate of one hydroxyl group of the copolymer to one molecule of the
latter. The product is further reacted with 2-hydroxyethyl
methacrylate at a rate of one hydroxyl group to one molecule. The
vinyl chloride-vinyl acetate copolymer resin thus obtained carries
the acrylic double bonds in a pendant fashion.
Examples of the polyisocyanate compounds useful for the above
purpose are 2,4-toluene diisocyanate, 2,6-toluene diisocyanate,
1,3-xylene diisocyanate, 1,4-xylene diisocyanate, m-phenylene
diisocyanate, p-phenylene diisocyanate, hexamethylene diisocyanate,
isophorone diisocyanate, "Desmodur L", and "Desmodur IL" (both made
by Farbenfabriken Bayer AG of West Germany).
The monomers having groups reactive with the isocyanate group and
also having radiation-setting, unsaturated double bonds include
hydroxyl-containing esters, such as 2-hydroxyethyl ester,
2-hydroxypropyl ester, and 2-hydroxyoctyl ester, of acrylic and
methacrylic acids; monomers having active hydrogen reactive with
the isocyanate group and also having acrylic double bonds, such as
acrylamide, methacrylamide, and n-methylolacrylamide; and monomers
having active hydrogen reactive with the isocyanate group and also
containing radiation-setting, unsaturated double bonds, such as
allyl alcohols, maleic acid esters of polyhydric alcohols, and
mono- and diglycerides of long-chain fatty acids having unsaturated
double bonds.
(II) A reaction product of a compound having at least one epoxy
group in the molecule and a monomer having groups reactive with the
epoxy group and also having radiation-setting, unsaturated double
bonds, at a rate of one molecule of the former to one or more
molecules of the latter, e.g., an epoxy-containing thermoplastic
resin obtained by radical polymerization with glycidyl alcohol, is
reacted with acrylic acid. Thus, by the ring-opening reaction of
the carboxyl and epoxy groups, a resin, prepolymer, or oligomer is
obtained which carries the acrylic double bonds as a pendant. Also,
maleic acid may be reacted so that a resin, prepolymer, or oligomer
having radiation-setting, unsaturated double bonds in the molecular
frame as a result of the ring-opening reaction of the carboxyl and
epoxy groups.
The compounds containing one or more epoxy groups in the molecule
include homopolymers of epoxy-containing acrylic ester and
methacrylic ester, such as glycidyl acrylate and glycidyl
methacrylate, or their copolymers with other polymerizable
monomers, such as "Epikote 828", "Epikote 1001", "Epikote 1007",
and "Epikote 1009"(all made by Shell Chemical Co.) which have
already been referred to in Section (V) above. Various other types
of epoxy resins may also be employed.
Among the useful monomers having the group reactive with the epoxy
group and also having radiation-setting, unsaturated double bonds
are carboxyl-containing acrylic monomers or acrylic and methacrylic
acids, and acrylic monomers having primary or secondary amino
groups, such as methylaminoethyl acrylate and methylaminoethyl
methacrylate. In addition, polybasic acid monomers having
radiation-setting, unsaturated double bonds, as of maleic acid,
fumaric acid, crotonic acid, and undecylenic acid, may be used.
(III) A reaction product of a compound containing at least one
carboxyl group in the molecule and a monomer having groups reactive
with the carboxyl group and also having radiation-setting,
unsaturated double bonds, at a rate of one molecule of the former
to one or more molecules of the latter. For example, a
carboxyl-containing thermoplastic resin obtained by solution
polymerization of methacrylic acid is reacted with glycidyl
methacrylate, and, in the same manner as in Section (II) above, a
resin, prepolymer, or oligomer in whose molecules have been
introduced acrylic double bonds by the ring-opening reaction of
carboxyl and epoxy groups is prepared.
The compounds that contain one or more carboxyl groups in the
molecule are, among the above-mentioned resins that contain
carboxyl groups in the molecular chain or at the end of a chain in
the molecule, polyesters and the homopolymers of monomers having
the radical polymerizability and containing carboxyl groups, such
as acrylic acid, methacrylic acid, maleic anhydride, and fumaric
acid, or their copolymers with other polymerizable monomers.
The monomers that have the group reactive with the carboxyl groups
and having radiation-setting, unsaturated double bonds are glycidyl
acrylate, glycidyl methacrylate, and the like.
Where a solvent is to be employed, a ketone, such as acetone,
methyl ethyl ketone, methyl isobutyl ketone, or cyclohexanone;
andester, such as ethyl acetate or butyl acetate; an alcohol, such
as methanol, ethanol, isopropanol, or butanol, which cannot be used
with the isocyanate thermosetting resin; tetrahydrofuran, dioxane,
or other compound having an ether bond; a solvent, such as dimethyl
formamide or vinylpyrrolidone; or an aromatic hydrocarbon diluent
or solvent, such as toluene or xylene, may be used.
The substrate to be coated may be the polyethylene terephthalate
film that is in wide use as a backing material for magnetic
recording media. Where heat resistance is an important
consideration, a polyimide film, polyamide imide film or the like
may be utilized. In the case of a polyester film as a thin base, it
is often used after monoaxial or biaxial stretching.
Fine magnetic powders which may be used in Examples to be given
later are finely divided .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3
O.sub.4, Co-doped .gamma.-Fe.sub.2 O.sub.3, Co-doped
.gamma.-Fe.sub.2 O.sub.3 -Fe.sub.3 O.sub.4 solid solution,
CrO.sub.2, Co-base-compound-coated .gamma.-Fe.sub.2 O.sub.3, and
Co-base-compound-coated Fe.sub.3 O.sub.4 (including those oxidized
to an intermediate state between itself and .gamma.-Fe.sub.2
O.sub.3). (The term "Co-base compounds" as used herein means cobalt
oxide, cobalt hydroxide, cobalt ferrite, cobalt ion-absorbates and
the like which enable the magnetic powder to take advantage of the
magnetic anisotropy of cobalt in improving its coercive force.)
Also, the magnetic powder may consist essentially of a
ferromagnetic metal element or elements, such as Co or Fe-Co,
Fe-Co-N, or Co-Ni system. Such a fine magnetic powder is prepared
in a number of ways, which include wet reduction of the starting
material with a reducing agent such as BH.sub.4, a treatment of the
iron oxide surface with a Si compound and subsequent wet reduction
with H.sub.2 gas or the like, and vacuum evaporation in a
low-pressure argon gas stream. Fine particles of monocrystalline
barium ferrite may be employed as well. The fine magnetic powder is
used in the form of acicular or granular particles, depending on
the application of the resulting magnetic recording medium.
In the field of high-bias hi-fi sound cassette tapes, video
cassette tapes, video tapes, master tapes for contact transfer
printing and the like. The technical progress in recent years has
been striking, and the market is fast growing. As a new addition to
this field, a high-performance tape possessing both extremely
desirable electromagnetic conversion characteristics and physical
reliability has now been provided, in accordance with the present
invention, by combining a binder of a radiation cross-linked type
or radiation polymerized and dried type with a fine magnetic
powder, especially a cobalt-modified acicular iron oxide
(cobalt-doped or Co-base-compound-coated type) advantageous for
high-density recording applications or with acicular fine alloy
particles having even greater coercive force.
With the binder type of the radiation-setting type or for the
manufacture of a magnetic recording medium, it is advisable to use
various additives usually employed for these applications, such as
an antistatic agent, lubricant, dispersant, and film-reinforcing
agent, to suit the particular end use.
Highly energetic rays for use in cross-linking the magnetic coating
may be radiant rays from a radiation accelerator as the source,
gamma radiation from Co.sup.60, or X-rays from an X-ray
generator.
The use of rays from a radiation accelerator is particularly
advantageous in view of the case of control of the dosage,
introduction into the process line, shield from the ionizing
radiation, etc.
With regard to the characteristics of radiation for use in curing
the magnetic coating, it is desirable from the standpoint of
transmissivity to adopt a radiation accelerator which operates with
an acceleration voltage of 100-750 kv, preferably 150-300 kv, and
effect the irradiation so that the radiation dosage may be in the
range of 0.2-20 megarads.
In the case of a magnetic tape, in particular, the film of coating
to be cured is thin, and therefore the adoption of the low-dosage
radiation accelerator made by Energy Science Inc. of the U.S.
("Electro-curtain system") or the equivalent is extremely
advantageous because of the ease with which the accelerator can be
installed on the tape coating line and the shield can be
established against secondary X-rays inside the apparatus.
Of course, the Van de Graff accelerator in extensive use as a
radiation accelerator may be employed instead.
In radiation cross-linking, exposure of the recording medium to
radiation in a stream of N.sub.2, He, or other inert gas is
important. A film of magnetic coating, which is very thickly filled
with a magnetic pigment, is highly porous in structure. When it is
exposed to radiation in air, O.sub.3 and the like produced by the
irradiation for the cross-linking of the binder component will have
an adverse effect, keeping the radicals formed in the polymer from
effectively acting for the cross-linking reaction. The adverse
effect is exercised not merely on the surface of the magnetic
coating layer but also deep into the porous film, thus hampering
the cross-linking of the binder.
For this reason it is essential to maintain an inert gas atmosphere
of N.sub.2, He, CO.sub.2, or the like with an oxygen concentration
of at most one percent around the portion to be exposed to the
highly energetic rays.
Next, examples of synthesis of radiation-sensitive binders will be
given below.
Process for Preparing Adducts of Tolylene Diisocyanate
(a) Synthesis of an acrylic modification product of vinyl
chloride-vinyl acetate copolymer resin (radiation-sensitive
modified resin):
A five-liter, four-necked flask is charged with 750 parts of
"Vinylite VAGH", 1250 parts of toluene, and 500 parts of
cyclohexanone. The charge is dissolved with the application of
heat. After the solution has been heated to 80.degree. C. 61.4
parts of 2-hydroxyethyl methacrylate adduct of tolylene
diisocyanate* is added. Then, 0.012 part each of tin octylate and
hydroquinone are added. The whole mixture is reacted in a stream of
N.sub.2 at 80.degree. C. for a period of time until an NCO reaction
rate of over 90% is attained. Following the conclusion of the
reaction, the product is cooled and diluted with 1250 parts of
methyl ethyl ketone. The synthesized product is used as a binder
(a).
In an N.sub.2 stream within a one-liter, four-necked flask, 348
parts of tolylene diisocyanate is heated to 80.degree. C., and then
260 parts of 2-hexaethylene methacrylate, 0.07 part of tin
octylate, and 0.05 part of hydroquinone are added dropwise while
the temperature inside the reactor is being controlled to be within
the range of 80.degree.-85.degree. C. After the addition, the
mixture is stirred at 80.degree. C. for 3 hours to conclude the
reaction. Following the conclusion of the reaction, the product is
taken out and cooled. In this way a white paste of a 2HEMA adduct
of TDI was obtained.
(b) Synthesis of an acrylic modification product of butyral resin
(radiation-sensitive modified resin):
One hundred parts of a butyral resin "BM-S" marketed by Sekisui
Chemical Co. is charged, together with 191.2 parts of toluene and
71.4 parts of cyclohexanone, into a five-liter, four-necked flask.
The charge is dissolved with heat, the temperature is increased to
80.degree. C., and 7.4 parts of the 2-hydroxyethyl methacrylate
adduct of tolylene diisocyanate* is added. Further, 0.015 part each
of tin octylate and hydroquinone are added, and the mixture is
allowed to react at 80.degree. C. in an N.sub.2 stream until an NCO
reaction rate in excess of 90%, is obtained. Following the
conclusion of the reaction, the product is cooled and diluted with
methyl ethyl ketone.
The synthesized product is used as a binder (b).
(c) Synthesis of an acrylic modification product of saturated
polyester resin (radiation-sensitive modified resin):
One hundred parts of Toyobo's "Vylon RV-200" is dissolved with heat
in 116 parts each of toluene and methyl ethyl ketone, the
temperature is raised to 80.degree. C., and 3.55 parts of the 2HEMA
adduct of TDI* and then 0.007 part each of tin octylate and
hydroquinone are added. The whole mixture is caused to react in an
N.sub.2 stream at 80.degree. C. up to an NCO reaction rate of over
90%.
(d) Synthesis of an acrylic modification product of epoxy resin
(radiation-sensitive modified resin):
In 50 parts each of toluene and MEK is dissolved 400 parts of Shell
Chemical's "Epikote 1007" with the application of heat. Then, 0.006
part of N,N-dimethylbenzylamine and 0.003 part of hydroquinone are
added to the solution, the mixture is heated to 80.degree. C., and
69 parts of acrylic acid is added dropwise. The whole mixture is
reached at 80.degree. C. until an acid value of less than 5 is
reached.
(e) Synthesis of an acrylic modification product of urethane
elastomer (radiation-sensitive elastomer):
A reaction vessel is charged with 250 parts of an urethane
prepolymer of diphenylmethane diisocyanate (MDI) having isocyanate
end groups ("Nippollan 4040" marketed by Nippon Polyurethane Ind.
Co.), 32.5 parts of 2HEMA, 0.07 part of hydroquinone, and 0.009
part of tin octylate. The mixture is dissolved by heating at
80.degree. C., 43,5 parts of TDI is added in drops while the
reaction vessel is being cooled so that a temperature in the range
of 80.degree.-90.degree. C. is maintained. Following the addition,
the mixture is allowed to react until an NCO reaction rate of over
95% is achieved.
(f) Synthesis of an acrylic modification product of polyether-type
modified elastomer with urethane end groups (radiation-sensitive
elastomer):
Two hundred and fifty parts of Nippon Polyurethane's "PTG-500",
32.5 parts of 2HEMA, 0.007 part of hydroquinone, and 0.009 part of
tin octylate are placed altogether into a reaction vessel. The
charge is dissolved by heating at 80.degree. C., and 43.5 parts of
TDI is added dropwise while cooling the reaction vessel to maintain
a temperature inside within the range of 80.degree.-90.degree. C.
Following the addition, a reaction is effected to achieve an NCO
reaction rate of more than 95%.
(g) Synthesis of an acrylic modification product of polybutadiene
elastomer (radiation-sensitive elastomer):
A reaction vessel is charged with 250 parts of Sinclair
Petrochemicals' low-molecular-weight, hydroxyl-end-group
polybutadiene "Poly-B-D Liquid Resin R-15", 32.5 parts of 2HEMA,
0.007 part of hydroquinone, and 0.009 part of tin octylate. The
charge is dissolved by heating at 80.degree. C., and 43.5 parts of
TDI is added dropwise while cooling the reaction vessel to maintain
a temperature inside within the range of 80.degree.-90.degree. C.
After the addition, the mixture is caused to react until an NCO
reaction rate of over 95% is attained.
(h) Synthesis of an allyl-group-introduced EBC resin (TDI-allyl
alcohol adduct):
After 348 parts of TDI has been heated in an N.sub.2 stream at
80.degree. C., 116 parts of allyl alcohol, 0.07 part of tin
octylate, and 0.02 part of hydroquinone are added in drops while
cooling and controlling the temperature inside the reaction vessel
within the range of 80.degree.-85.degree. C. After the dropping,
the mixture is reacted with stirring at 80.degree. C. for 3
hours.
(Example of resin synthesis)
Fifteen parts of 2-hydroxyethyl methacrylate, 35 parts of butyl
methacrylate, and 37.5 parts each of toluene and MEK are placed in
a reaction vessel, heated to 80.degree. C., and then 45 parts of
2HEMA, 105 parts of butyl methacrylate, 6 parts of benzoyl
peroxide, and 112.5 parts of toluene are added dropwise. The whole
mixture is reacted at 80.degree.-90.degree. C. for 4 hours. To 195
parts of the reaction product, 46.6 parts of TDI-allyl alcohol
adduct and then 0.01 part each of tin octylate and hydroquinone are
added. The mixture is reacted at 80.degree. C. up to an NCO
reaction rate in excess of 90%.
(i) Synthesis of unsaturated polyester-type EBC resin:
A reaction vessel was charged with 136 parts of dimethyl sebacate,
12.2 parts of dimethyl adipate, 64.8 parts of dimethyl maleate, 73
parts of neopentyl glycol, 74 parts of 1,6-hexanediol, and 10 parts
of tetra-n-butyl titanate. After a demethanolizing reaction at
180.degree. C. in an N.sub.2 stream, the resultant is heated to
240.degree.-260.degree. C. and subjected to a condensation reaction
under a reduced pressure of 0.5-1 mmHg. In this manner a resin
closely resembling an internally plasticized elastomer
resulted.
The invention will now be described in connection with examples in
which a radiation-setting titanium coupling agent (e.g., Kenrich's
"KR-7" or "KR-55") was added as a dispersant to each reaction
mixture. Examples 4 through 7 illustrate a procedure in common
wherein magnetic particles are wetted with a coupling agent and
then are mixed and dispersed with a binder.
EXAMPLE 4
A composition consisting of
______________________________________ Cobalt-deposited acicular
.gamma.-Fe.sub.2 O.sub.3 120 parts (major axis 0.4.mu., minor axis
0.05.mu., by weight Hc 600 Oe) Carbon black (for antistatic use, 5
parts "Mitsubishi Carbon Black Ma-600") by weight .alpha.-Al.sub.2
O.sub.3 powder (particle size 0.5.mu.) 2 parts by weight Titanium
coupling agent (Kenrich's "KR-7") 3 parts by weight Solvent 100
parts (methyl ethyl ketone/toluene 50/50) by weight
______________________________________
was mixed on a ball mill for 3 hours, so that the acicular iron
oxide particles were thoroughly wetted with the titanium coupling
agent.
Next, a binder mixture consisting of
______________________________________ Acrylic
double-bond-introduced, 10 weight parts saturated polyester resin
(c) (on solids basis) Acrylic double-bond-introduced 10 weight
parts vinyl chloride-vinyl acetate copolymer (on solids basis) (a)
Acrylic double-bond-introduced 10 weight parts polyether urethane
elastomer (f) (on solids basis) Solvent 200 weight parts (methyl
ethyl ketone/toluene 50/50) (on solids basis) Lubricant (higher
fatty acid-modified 3 weight parts silicone oil) (on solids basis)
______________________________________
was mixed well and dissolved. The resultant was placed into the
ball mill where the magnetic powder had been treated in advance,
and the two were again mixed and dispersed for 42 hours.
The magnetic coating material thus obtained was applied to a 15
.mu.-thick polyester film, magnetically oriented on a (1600-gauss)
permanent magnet, and the solvent was dried away by an infrared
lamp or hot air. The coating surface was smoothened and the film
was hardened by irradiation with radiant rays in an N.sub.2
atmosphere by ESI's "Electro-curtain" type radiation accelerator at
an acceleration voltage of 150 keV with an electrode current of 20
mA to a total dosage of 10 mrads.
The tape thus obtained was slitted into a ribbon 1/2-in. wide as a
video tape (Specimen 4).
The cross-linking of this magnetic film is understood to have
resulted from the combination of cross-linking by radicalization of
the acrylic double bonds and cross-linking by the radicals formed
in the molecular chains of vinyl chloride and vinyl acetate
(possibly due to HCl removal but yet to be clarified).
Comparative Example 3
A composition consisting of
______________________________________ Cobalt-deposited acicular
.gamma.-Fe.sub.2 O.sub.3 120 parts (major axis 0.4.mu., minor axis
0.05.mu., by weight Hc 600 Oe) Carbon black (for antistatic use, 5
parts "Mitsubishi Carbon Black MA-600") by weight .alpha.-Al.sub.2
O.sub.3 powder (particle size 0.5.mu.) 2 parts by weight Silane
coupling agent (UCC's "A-189") 3 parts by weight Solvent 100 parts
(methyl ethyl ketone/toluene 50/50) by weight
______________________________________
was mixed on a ball mill for 3 hours, so that the acicular iron
oxide particles were thoroughly wetted with the silane coupling
agent. Next, a binder mixture consisting of
______________________________________ Acrylic
double-bond-introduced, 10 weight parts saturated polyester resin
(c) (on solids basis) Acrylic double-bond-introduced 10 weight
parts vinyl chloride-vinyl acetate copolymer (on solids basis) (a)
Acrylic double-bond-introduced 10 weight parts polyether urethane
elastomer (f) (on solids basis) Solvent 200 weight parts (methyl
ethyl ketone/toluene 50/50) (on solids basis) Lubricant (higher
fatty acid-modified 3 weight parts silicone oil) (on solids basis)
______________________________________
was mixed well and dissolved. The resultant was placed into the
ball mill where the magnetic powder had been treated in advance,
and the two were again mixed and dispersed for 42 hours.
The magnetic coating material thus obtained was applied to a 15
.mu.-thick polyester film, magnetically oriented on a (1600-gauss)
permanent magnet, and the solvent was dried away by an infrared
lamp or hot air. The coating surface was smoothened and the film
was hardened by irradiation with radiant rays in an N.sub.2
atmosphere by ESI's "Electro-curtain" type radiation accelerator at
an acceleration voltage of 150 keV with an electrode current of 20
mA to a total dosage of 10 mrads.
The tape thus obtained was slitted into a ribbon 1/2-in. wide as a
video tape (Specimen C).
The cross-linking of the magnetic film is understood to have
resulted from the combination of cross-linking by radicalization of
the acrylic double bonds and cross-linking by the radicals formed
in the molecular chains of vinyl chloride and vinyl acetate
(possibly due to HCl removal but yet to be clarified).
FIG. 1 is a graph showing the rates of attenuation (on still
reproduction) of signals with respect to the reproduction output,
as measured by recording signals on the video tape specimens by a
video tape recorder (Matsushita Electric's "NV-3120") for open
reels conforming to the EIAJ unified standards and then by
reproducing the still images with a tension of 200 grams applied on
the take-up side by a spring balancer.
As can be seen from the graph, the cross-linking of the binder by
irradiation gives a coating film of a tough structure and markedly
reduces the rate of signal attenuation, regardless of the rigorous
abrasive condition with a relative velocity of the magnetic film
and the head as high as 11 meters a second.
FIG. 2 is a graphic representation of changes in friction of test
video tapes with running time. Each tape was held for five days
under changing conditions in five cycles, each beginning with a
temperature of -10.degree. C. and a relative humidity of 0% and
ending with 60.degree. C. and 80%. After this period, the specimen
was kept still at room temperature for 24 hours. The tape was then
put on the same video tape recorder as used for the still
reproduction test, a tension analyzer marketed by Japan Automatic
Control Co., Model 1VA-500, was set between the head drum and the
pinch roller of the recorder, and the changes in tension on the
take-up side of the test tape with running time were measured.
This test permits evaluation of not only the friction coefficient
level of the magnetic film itself of each test tape but also the
degree of deterioration of tape running quality due to exudation of
the low-molecular-weight components from the magnetic film, and
stability of the tape against the environmental conditions such as
temperature and humidity.
Also, as indicated in Table 4, it has been found that the frequency
of output is decreased and the bonding strength improved by the
radiation cross-linking. Thus, the dropout problem has now been
solved by this invention.
TABLE 4 ______________________________________ Electromagnetic No.
of Bond Spec- Surface convern. charac..sup.(2) dropouts
str..sup.(4) imen quality.sup.(1) 4 MHz Y S/N per min..sup.(3) (g)
______________________________________ 4 12.0 0 0 0.3 80 C 7.5 -12
dB -8.0 dB 6 15 ______________________________________ Remarks:
.sup.(1) The surface gloss value as measured on the basis of a
reference glass plate which is set at zero decibel (dB). .sup.(2)
Determined with Matsushita Electric's video tape recorder, Model
National Maclord 6600. .sup.(3) Determined with Matsushita
Electric's video tape recorder, Model National Maclord 6600.
.sup.(4) Bonding strength as measured by a test for stripping the
coating away from the base under tension.
As compared with Specimen C, Specimen 4 was confirmed to have been
stably uniformalized in cross-linking by irradiation, with superior
surface quality and improved electromagnetic conversion
characteristics.
EXAMPLE 5
A composition consisting of
______________________________________ Acicular magnetic powder of
Fe alloy 120 parts (major axis 0.3.mu., minor axis by weight
0.04.mu., Hc 1100 Oe) Radiation-setting titanium coupling 0.6 part
agent (Kenrich's "KR-55") Solvent 100 parts (methyl ethyl
ketone/toluene 50/50) ______________________________________
was mixed by a powerful mixer for 3 hours, so that the fine
particles of magnetic alloy were thoroughly wetted with the
titanium coupling agent. Next, a mixture consisting of
______________________________________ Acrylic
double-bond-introduced 18 weight parts butyral resin (b) (on solids
basis) Acrylic double-bond-introduced 12 weight parts urethane
elastomer (e) (on solids basis) Solvent 200 weight parts (methyl
ethyl ketone/toluene 50/50) (on solids basis) Lubricant (higher
fatty acid) 3 weight parts (on solids basis)
______________________________________
was mixed well and dissolved.
The resultant was thoroughly mixed with the pretreated magnetic
powder by a high speed mixer for 70 minutes and then mixed and
dispersed by a sand grinding mill for a further period of 4
hours.
The magnetic coating material thus prepared was applied to a 12
.mu.-thick polyester film. After magnetic field orientation,
solvent drying, and surface smoothening, the coated film was
exposed to radiation in an N.sub.2 gas atmosphere in an
"Electro-curtain" type radiation accelerator at an acceleration
voltage of 150 keV with an electrode current of 10 mA to a total
dosage of 5 mrads.
The tape so obtained was slitted into a ribbon 3.8 mm wide as an
alloy audio cessette tape (Specimen 5).
Comparative Example 4
A composition consisting of
______________________________________ Acicular magnetic powder of
Fe alloy 120 parts (major axis 0.3.mu., minor axis by weight
0.04.mu., Hc 1100 Oe) Silane coupling agent (UCC's "A 189") 2 parts
by weight Solvent 100 parts (methyl ethyl ketone/toluene 50/50) by
weight ______________________________________
was mixed on a ball mill for 3 hours, and the acicular magnetic
iron oxide particles were thoroughly wetted with the silane
coupling agent.
Next, a binder mixture consisting of
______________________________________ Acrylic
double-bond-introduced, 10 weight parts saturated polyester resin
(c) (on solids basis) Acrylic double-bond-introduced 10 weight
parts vinyl chloride-vinyl acetate copolymer (on solids basis) (a)
Acrylic double-bond-introduced 10 weight parts polyether urethane
elastomer (f) (on solids basis) Solvent 200 weight parts (methyl
ethyl ketone/toluene 50/50) (on solids basis) Lubricant (higher
fatty acid-modified 3 weight parts silicone oil) (on solids basis)
______________________________________
was mixed well and dissolved. The resultant was placed into the
ball mill where the magnetic powder had been treated in advance,
and the two were again mixed and dispersed for 42 hours.
The magnetic coating material thus obtained was applied to a 15
.mu.-thick polyester film, magnetically oriented on a (1600-gauss)
permanent magnet, and the solvent was dried away by an infrared
lamp or hot air. The coating surface was smoothened and the film
was hardened by irradiation with radiant rays in an N.sub.2
atmosphere by ESI's "Electro-curtain" type radiation accelerator at
an acceleration voltage of 150 keV with an electric current of 20
mA to a total dosage of 10 mrads.
The tape thus obtained was slitted into a ribbon 1/2-in. wide as a
video tape (Specimen D).
Specimen D was compared in tests with Specimen 5. The results were
as shown in Table 5.
TABLE 5 ______________________________________ Electromag. convn.
charac..sup.(3) MoL MoL MoL Surface 33 8 16 Tape Recipro. run Spec-
quality Hz KHz KHz squeal.sup.(4) durability.sup.(5) imen.sup.(1)
(dB) (dB) (dB) (dB) (hr) (No. of pass)
______________________________________ 5 12.4 +3.5 +6.5 +12.0 30
Over 200 D 8.5 +2.5 +3.0 +8.5 10 Stopped after 50 passes
______________________________________ Remarks: .sup.(1) After
radiation setting. .sup.(2) The surface gloss value as measured on
the basis of a reference glass plate which is set at zero decibel
(dB). .sup.(3) Determined with Nakamichi Research Institute's
cassette deck, Model Nakamichi 582, in the metal position. .sup.(4)
Determined at 40.degree. C. and 80% RH with Matsushita
Communication Ind.'s car stereo set, Model National CX318. .sup.(5)
Determined at 40.degree. C. and 60% RH with Matsushita
Communication's car stereo set, Model CX1147D.
The radiation-sensitive elastomer component used in this Example of
the invention can be of a low molecular weight because of its
subjection to radiation cross-linking. Hence it is affinitive for
the alloy magnetic particles and imparts the magnetic coating
material with an excellent surface-forming property after
application.
Consequently, the tape so formed possessed very high sensitivity
over the MoL range from the low frequency of 333 Hz up to the high
frequency of 16 KHz.
As measures of reliability, the period of running time the tape
took to begin squealing and the durability of the tape with
reciprocating travel from reel to reel past the head of a car
stereo set were determined. In these and other tests it was
confirmed that the tape according to the invention had greater
durability and reliability in unfavorable environments, such as
high temperatures and high humidities.
EXAMPLE 6
______________________________________ Fe.sub.2 O.sub.3 (major axis
0.8.mu., minor axis 0.2.mu., 120 parts Hc 300 Oe) by weight Carbon
black (for antistatic use, 5 parts "Mitsubishi Carbon Black
MA-600") by weight .alpha.-Al.sub.2 O.sub.3 powder (particle size
0.5.mu.) 2 parts by weight Titanium coupling agent (Kenrich's 3.6
parts "KR-11") by weight Solvent 100 parts (methyl ethyl
ketone/toluene 50/50) by weight
______________________________________
These components were mixed up by a ball mill for 3 hours, and the
the magnetic iron oxide was thoroughly wetted with the titanium
coupling agent.
Next,
______________________________________ Acrylic
double-bond-introduced 15 parts eposy resin (d) by weight Acrylic
double-bond-introduced 15 parts polybutadiene elastomer (g) by
weight Solvent 200 parts (methyl ethyl ketone/toluene 50/50) by
weight Lubricant (fluorine oil, E.I. du Pont 3 parts de Nemours'
"Kritox") by weight ______________________________________
were mixed well and dissolved.
The resultant was placed into the ball mill where the magnetic
powder had been treated in advance, and the two were again mixed
and dispersed for 42 hours.
The magnetic coating material thus prepared was applied to one side
of a 188 .mu.-thick polyester film to form a coating film about
10.mu. thick, and the coating was dried, and then the coated
surface was smoothened. The coating film was hardened by
irradiation in an N.sub.2 gas atmosphere by an "Electro-curtain"
type radiation accelerator at an acceleration voltage of 175 keV
with an electrode current of 15 mA to a total dosage of 2
mrads.
A disk (about 65 mm in diameter) was blanked out of the resulting
roll, and magnetic disk (Specimen 6) was obtained.
The same coating material was applied on a 75 .mu.-thick polyester
film and after a similar process, a sealless commutation ticket of
a given size was cut out of the coated film.
EXAMPLE 7
______________________________________ Fe.sub.2 O.sub.3 (major axis
0.8.mu., minor axis 0.2.mu., 120 parts Hc 300 Oe) by weight Carbon
black (for antistatic use, 5 parts "Mitsubishi Carbon Black
MA-600") by weight .alpha.-Al.sub.2 O.sub.3 powder (particle size
0.5.mu.) 2 parts by weight Titanium coupling agent (Kenrich's 6
parts "KR-39CS") by weight Solvent 100 parts (methyl ethyl
ketone/toluene 50/50) by weight
______________________________________
These components were mixed up by a ball mill for 3 hours, and the
magnetic iron oxide was thoroughly wetted with the titanium
coupling agent.
Next,
______________________________________ Allyl-group-introduced 15
weight parts methacrylic resin (on solids basis)
Internally-plasticized 15 weight parts unsaturated polyester resin
(on solids basis) Solvent 200 weight parts (methyl ethyl
ketone/toluene 50/50) (on solids basis) Lubricant (fatty
acid-modified siloxane) 3 weight parts (on solids basis)
______________________________________
were mixed well and dissolved. The resultant was placed into the
ball mill where the magnetic powder had been treated beforehand,
and the two were again mixed for 42 hours.
The magnetic coating material thus prepared was applied to one side
of a 188 .mu.-thick polyester film to form a coating film about 10
.mu.-thick, and the coating was dried, and then the coated surface
was smoothened. The coating film was hardened by irradiation in a
CO.sub.2 gas atmosphere by an "Electro-curtain" type radiation
accelerator at an acceleration voltage of 175 keV with an electrode
current of 15 mA to a total dosage of 2 mrads.
A disk (about 65 mm in diameter) was blanked out of the resulting
roll, and a magnetic disk (Specimen 7) was obtained.
Each of the test magnetic disks was set on a recorder-reproducer
and was driven to run at a speed of about one meter per second in
sliding contact with the magnetic head (at a pad pressure of 40
g/cm.sup.2), and the time elapsed until the cumulative number of
dropouts reached 1000 was measured.
The results of time measurements and the surface conditions at the
ends of the periods are summarized in Table 6.
COMPARATIVE EXAMPLES 5 & 6
The procedures of Examples 6 and 7 were repeated, respectively,
with the exception that the titanium coupling agents were replaced
by a silane coupling agent (UCC's "A-189"), and similar pieces of
magnetic recording medium were obtained. As Specimens E and F,
their test results and appearances are also given in Table 6.
TABLE 6 ______________________________________ Specimen (after ex-
Running Surface posure to radiation) time (hr) condition
______________________________________ 6 Over 50 Good E Failed
Serious in 30 scratches 7 Over 50 Good F Failed Serious in 30
scratches ______________________________________
The table makes it certain that the magnetic coating attains
strength on exposure to radiation.
The specimen of Example 6 as a sealless commutation ticket was
tested for gate endurance, together with Comparative Specimen E.
The results are shown in FIG. 3.
The curves represent the attenuation rates (in Em) of the peak
voltages of the reproduction outputs after repeated passes through
the gate, on the basis of the initial reproduction output peak
voltage as 100%. Usually, the point where the reproduction output
peak voltage has dropped from the initial standard output voltage
by more than 25% is judged to be the end of the ticket life.
As shown in FIG. 3, the pulse signal peak voltage levels up to the
maximum number of repeated passes of 30000 were observed.
It was confirmed that the decline of the output with the frequency
of reproduction by the test medium was reduced to a minimum and a
remarkable improvement in this respect was achieved by the
radiation cross-linking in accordance with the invention.
Now, modifications of the invention in which the magnetic particles
are coated with a radiation-setting titanium coupling agent
(Kenrich's "KR-7" or "KR-55") will be described in connection with
Examples 8 through 11.
EXAMPLE 8
A composition consisting of
______________________________________ Cobalt-deposited, acicular
.alpha.-Fe.sub.2 O.sub.3 120 parts (major axis 0.4.mu., minor axis
0.05.mu., by weight Hc 600 Oe) Titanium coupling agent 2.5 parts
(Kenrich's "KR-7") by weight Solvent 500 parts (methyl ethyl
ketone/toluene 50/50) by weight
______________________________________
was mixed in the same way as described in Example 3 to coat the
magnetic particles with the titanium coupling agent. Using the
coated powder, a composition of
______________________________________ Cobalt-deposited, acicular
coated 120 parts .alpha.-Fe.sub.2 O.sub.3 by weight Carbon black
(for antistatic use, 5 parts "Mitsubishi Carbon Black MA-600") by
weight .alpha.-Al.sub.2 O.sub.3 powder (particle size 0.5.mu.) 2
parts by weight Solvent 100 parts (methyl ethyl ketone/toluene
50/50) by weight ______________________________________
was mixed for thorough dispersion by a ball mill for 3 hours.
Next, a binder mixture consisting of
______________________________________ Acrylic
double-bond-introduced, 10 weight parts saturated polyester resin
(c) (on solids basis) Acrylic double-bond-introduced 10 weight
parts vinyl chloride-vinyl acetate copolymer (on solids basis) (a)
Acrylic double-bond-introduced 10 weight parts polyether urethane
elastomer (f) (on solids basis) Solvent 200 weight parts (methyl
ethyl ketone/toluene 50/50) (on solids basis) Lubricant (higher
fatty acid-modified 3 weight parts silicone oil) (on solids basis)
______________________________________
was mixed well and dissolved. The resultant was placed into the
ball mill that had already treated the magnetic powder, and the two
were again mixed and dispersed for 42 hours.
The magnetic coating material thus obtained was applied to a
15.mu.-thick polyester film, magnetically oriented on a
(1600-gauss) permanent magnet, and the solvent was dried away by an
infrared lamp or hot air. The coating surface was smoothened and
the film was hardened by irradiation with radiant rays in an
N.sub.2 atmosphere by ESI's "Electro-curtain" type radiation
accelerator at an acceleration voltage of 150 keV with an electric
current of 20 mA to a total dosage of 10 mrads.
The tape thus formed was slitted into a ribbon 1/2-in. wide as a
video tape (Specimen 8).
The cross-linking of this magnetic film is understood to have
resulted from the combination of cross-linking by radicalization of
the acrylic double bonds and cross-linking by the radicals formed
in the molecular chains of vinyl chloride and vinyl acetate
(possibly due to HCl removal but yet to be clarified).
FIG. 4 is a graph showing the rates of attenuation (on still
reproduction) of signals with respect to the reproduction output,
as measured by recording signals on the video tape specimen and
comparative specimens by a video tape recorder (Matsushita
Electric's "NV-3120") for open reels conforming to the EIAJ unified
standards and then by reproducing the still images with a tension
of 200 grams applied on the take-up side by a spring balancer.
As can be seen from the graph, the cross-linking of the binder by
irradiation gives a coating film of a tough structure and markedly
reduces the rate of signal attenuation, regardless of the rigorous
abrasive condition with a relative velocity of the magnetic film
and the head as high as 11 meters a second.
FIG. 5 is a graphic representation of changes in friction of the
test video tape and a comparative specimen with running time. Each
tape was held for five days under changing conditions in five
cycles, each beginning with a temperature of -10.degree. C. and a
relative humidity of 0% and ending with 60.degree. C. and 80%.
After this period, the specimen was kept still at room temperature
for 24 hours. The tape was then put on the same video tape recorder
as used for the still reproduction test, a tension analyzer
marketed by Japan Automatic Control Co., Model 1VA-500, was set
between the head drum and the pinch roller of the recorder, and the
changes in tension on the take-up side of the test tape with
running time were measured.
This test permits evaluation of not only the friction coefficient
level of the magnetic film itself of each test tape but also the
degree of deterioration of tape running quality due to exudation of
the low-molecular-weight components from the magnetic film, and
stability of the tape against the environmental conditions such as
temperature and humidity.
As will be understood from these graphs, the radiation cross-linked
tapes have low friction coefficients. The low-molecular-weight
elastomer component of the coating composition is thoroughly
cross-linked and will not exude to the tape surface. The tapes run
stably despite changes in temperature and humidity. Moreover, the
tape (Specimen 8) of Example 8 had a greater inter-film strength
than the tape (Specimen 4) of Example 4 where the titanium coupling
agent was not applied but merely added to the magnetic powder. Test
results indicative of this are given in Table 7. The table also
carries the test results of the tape of Comparative Example 3 which
used a silane coupling agent. The latter specimen is designated C'
because it came from a different production batch in the
comparative example.
TABLE 7 ______________________________________ Electromagnetic No.
of Bond. Spec- Surface convern. charac..sup.(2) dropouts
str..sup.(4) imen quality.sup.(1) 4 MHz Y S/N per min..sup.(3) (g)
______________________________________ 8 14.0 +0.7 +2.5 0.1 100 C'
8.0 -10 -7.0 5 20 4 12.0 0 0 0.3 80
______________________________________ Remarks: .sup.(1) The
surface gloss value as measured on the basis of a reference glass
plate which is set at zero decibel (dB). .sup.(2) Determined with
Matsushita Electric's video tape recorder, Model National Maclord
6600. .sup.(3) Determined with Matsushita Electric's video tape
recorder, Model National Maclord 6600. .sup.(4) Bonding strength as
measured by a test for stripping the coating away from the base
under tension.
EXAMPLE 9
______________________________________ Acicular magnetic particles
of Fe alloy 120 parts (major axis 0.3.mu., minor axis 0.04.mu., by
weight Hc 1100 Oe) Titanium coupling agent (Kenrich's 0.6 parts
"KR-55") by weight Water 500 parts by weight
______________________________________
In the same manner as described in Example 3, these components were
mixed, heated, and dried, so that the magnetic particles were
coated with the titanium coupling agent.
For use with the coated magnetic particles, a mixture consisting
of
______________________________________ Acrylic
double-bond-introduced 18 weight parts butyral resin (b) (on solids
basis) Acrylic double-bond-introduced 12 weight parts urethane
elastomer (e) (on solids basis) Solvent 200 weight parts (methyl
ethyl ketone/toluene 50/50) (on solids basis) Lubricant (higher
fatty acid) 3 weight parts (on solids basis)
______________________________________
was mixed well and dissolved.
The resultant was thoroughly mixed with the pretreated magnetic
particles by a high speed mixer for 70 minutes, and the mixture was
further mixed and dispersed by a sand grinding mill for 4
hours.
The magnetic coating material thus prepared was applied to a
12.mu.-thick polyester film. After magnetic field orientation,
solvent drying, and surface smoothening, the coated film was
exposed to radiation in an N.sub.2 gas atmosphere in an
"Electro-curtain" type radiation accelerator at an acceleration
voltage of 150 keV with an electrode current of 10 mA to a total
dosage of 5 mrads.
The tape so obtained was slitted into a ribbon 3.8 mm wide as an
alloy audio cassette tape (Specimen 9).
The tape was compared with the tape (Specimen 5) of Example 5 in
which the titanium coupling agent was simply added to the coating
composition, and the results as shown in Table 8 were obtained.
TABLE 8 ______________________________________ Electromag. Recipro.
Sur- Conv. Charac..sup.(2) run De- face MoL MoL MoL Tape durability
posit Spec- qual- 333 3 16 squeal.sup.(3) (No. of on imen
ity.sup.(1) Hz KHz KHz (hr) pass head.sup.(5)
______________________________________ 9 14.0 +4.0 +7.0 +12.5 30
>200 4 5 12.5 +3.5 +6.5 +12.0 30 >200 3
______________________________________ Remarks: .sup.(1) The
surface gloss value as measured on the basis of a reference glass
plate which is set at zero decibel (dB). .sup.(2) Determined by
means of Nakamichi Research Institute's cassette deck, Model
Nakamichi 582 in the metal position. .sup.(3) Determined by means
of Nakamichi Research Institute's cassette deck, Model Nakamichi
582 in the metal position. .sup.(4) Determined by means of
Nakamichi Research Institute's cassette deck, Model Nakamichi 582
in the metal position. .sup.(5) Determined by means of Nakamichi
Research Institute's cassette deck, Model Nakamichi 582 in the
metal position.
As will be apparent from Table 8, the radiation-sensitive elastomer
component used in Example 9 can be of a low molecular weight
because of its subjection to radiation cross-linking. Hence it is
affinitive for the magnetic alloy particles and imparts the
magnetic coating material with an excellent surface-forming
property after application, allowing the tape to have a very smooth
surface and a high residual magnetic flux density.
Thus, a tape of every high sensitivity over the MoL ranges from the
low frequency of 333 Hz to the high frequency of 16 KHz was
obtained. Furthermore, because the surface quality was excellent
and the electromagnetic conversion characteristics and inter-film
strength were improved, the amount of deposit on the head of the
video tape recorder decreased.
EXAMPLE 10
______________________________________ .gamma.-Fe.sub.2 O.sub.3
(major axis 0.8.mu., minor axis 120.mu., parts Hc 300 Oe) by weight
Titanium coupling agent (Kenrich's 3.6 parts "KR-55") by weight
Solvent 500 parts (methyl ethyl ketone/toluene 50/50) by weight
______________________________________
These components were mixed, heated, and dried, so that the
magnetic particles were coated with the titanium coupling
agent.
Next,
______________________________________ Acrylic
double-bond-introduced 15 parts epoxy resin (d) by weight Acrylic
double-bond-introduced 15 parts polybutadiene elastomer (g) by
weight Solvent 200 parts (methyl ethyl ketone/toluene 50/50) by
weight Lubricant (fluorine oil, E.I. du Pont 3 parts de Nemours
"Kritox") by weight ______________________________________
were mixed well and dissolved to obtain a mixture.
The mixture was placed into a ball mill together with
______________________________________ Titanium coupling
agent-coated 120 parts .alpha..alpha.-Fe.sub.2 O.sub.3 by weight
Carbon black (for antistatic use, 5 parts "Mitsubishi Carbon Black
MA-600") by weight .alpha.-Al.sub.2 O.sub.3 (particle size 0.5.mu.)
2 parts by weight Solvent 100 parts (methyl ethyl ketone/toluene
50/50) by weight ______________________________________
and the whole mixture was again mixed and dispersed for 42
hours.
The magnetic coating material thus prepared was applied to one side
of a 188.mu.-thick polyester film to form a coating film about
10.mu. thick, and the coating was dried, and then the coated
surface was smoothened. The coating film was hardened by
irradiation in an N.sub.2 gas atmosphere by an "Electro-curtain"
type radiation accelerator at an acceleration voltage of 175 keV
with an electrode current of 15 mA to a total dosage of 2
mrads.
A disk (about 65 mm in diameter) was blanked out of the resulting
roll, and a magnetic disk (Specimen 10) was obtained.
EXAMPLE 11
______________________________________ Fe.sub.2 O.sub.3 (major axis
0.8.mu., minor axis 0.2.mu., 120 parts Hc 300 Oe) by weight
Titanium coupling agent (Kenrich's "KR-7"). 6 parts by weight
Solvent 100 parts (methyl ethyl ketone/toluene 50/50) by weight
______________________________________
These components were mixed, heated, and dried. The magnetic
particles were coated with the titanium coupling agent. Next, a
mixture of
______________________________________ Allyl-group-introduced 15
weight parts methacrylic resin (on solids basis)
Internally-plasticized, 15 weight parts unsaturated polyester resin
(on solids basis) Solvent 200 weight parts (methyl ethyl
ketone/toluene 50/50) (on solids basis) Lubricant (fatty
acid-modified) 3 weight parts siloxane (on solids basis)
______________________________________
were mixed well and dissolved.
The resultant was thoroughly mixed for dissolution with a mixture
consisting of:
______________________________________ Titanium coupling
agent-coated 120 parts .gamma.Fe.sub.2 O.sub.3 by weight Carbon
black (for antistatic use, 5 parts "Mitsubishi Carbon Black
MA-600") by weight .alpha.-Al.sub.2 O.sub.3 (particle size 0.5.mu.)
2 parts by weight Solvent 100 parts (methyl ethyl ketone/toluene
50/50) by weight ______________________________________
The resultant was placed into the ball mill where the magnetic
powder had been treated in advance, and again mixing and dispersion
were effected for 42 hours.
The magnetic coating material thus prepared was applied to one side
of a 188.mu.-thick polyester film to form a coating film about
10.mu. thick, and the coating was dried, and then the coated
surface was smoothened. The coating film was hardened by
irradiation in a CO.sub.2 gas atmosphere by an "Electro-curtain"
type radiation accelerator at an acceleration voltage of 175 keV
with an electrode current of 15 mA to a total dosage of 2
mrads.
A disk (about 65 mm in diameter) was blanked out of the resulting
roll, and a magnetic disk (Specimen 11) was obtained.
In order to find out the effects of varied treating conditions upon
the properties of magnetic coating layers, magnetic disks
(Specimens 6' and 7') were made by the same procedures as described
in Example 6 (with the exception that the 3.6 parts of the titanium
coupling agent, Kenrich's "KR-11", was replaced by 3 parts of
Kenrich's "KR-55") and in Example 7 (with the exception that the 6
parts by weight of the titanium coupling agent, Kenrich's
"KR-39CS", was replaced by 3 parts of Kenrich's "KR-7"). These
comparative specimens and the magnetic disks of the foregoing
examples (Specimens 10 and 11) were tested for their performances.
Each test disk was set on a recorder-reproducer and was driven to
run at a speed of about one meter per second in sliding contact
with the magnetic head (at a pad pressure of 40 g/cm.sup.2), and
the time required for the dropouts to reach a cumulative number of
1000 was measured.
The results of time measurements and the surface conditions at the
ends of the periods are summarized in Table 9.
TABLE 9 ______________________________________ Running Surface
Deposit Specimen time condition on head
______________________________________ 10 >50 min. Good 4.5 6'
>50 min. Good 4 11 >50 min. Good 4.5 7' >50 min. Good 4
______________________________________
As is manifest from the table, Specimens 10 and 11 formed less
deposits on the head than Specimens 6' and 7' did, proving that the
former two had superior coating films.
* * * * *